scholarly journals Apomixis in flowering plants: an overview

2003 ◽  
Vol 358 (1434) ◽  
pp. 1085-1093 ◽  
Author(s):  
A. J. Richards
Keyword(s):  
Genetic Modification ◽  
Genetic Load ◽  
Flowering Plants ◽  
Endosperm Nucleus ◽  
Linkage Groups ◽  
Primary Endosperm Nucleus ◽  
Genomic Imbalance ◽  
Perennial Plants ◽  
Somatic Recombination ◽  
Recessive Mutant

Apomixis is a common feature of perennial plants, which occurs in ca . 60% of the British flora, but has been largely ignored by reproductive theoreticians. Successful individuals may cover huge areas, and live to great ages, favoured by ‘symmetrical’ selection. Apomixis is favoured by colonizing modes, for instance post–glacially. Despite its theoretical advantages, apomixis usually coexists with sexuality, suggesting ‘hidden’ disadvantages. Agamospermy (apomixis by seed) is relatively uncommon, but gains from the attributes of the seed. It pays agamospermy genes, which discourage recombination, to form co–adapted linkage groups, so that they become targets for disadvantageous recessive mutant accumulation. Consequently, agamospermy genes cannot succeed in diploids and agamosperms are hybrid and highly heterotic. Agamospermous endosperm may suffer from genomic imbalance, so that nutritious ovules, which can support embryos without endosperm, may be preadapted for agamospermy. When primary endosperm nucleus fertilization (‘pseudogamy’) continues as a requirement for many aposporous agamosperms, selfing sex becomes preadaptive and archesporial sex remains an option. Apomictic populations can be quite variable although apomictic families are much less variable than sexuals. Only in some diplosporous species does sex disappear completely, and in those species some release of variability may persist through somatic recombination. The search for an agamospermy gene suitable for genetic modification should target fertile sexuals with a single localized agamospermy ( A ) gene, which therefore lack a genetic load. The A gene should coexist alongside sexuality, so that it would be easy to select seedlings of sexual and asexual origins. Plants with sporophytic agamospermy provide all these attributes.

scholarly journals EMBRYOLOGY OF INTERSPECIFIC CROSSES IN MELILOTUS

1954 ◽  
Vol 32 (3) ◽  
pp. 447-465 ◽  
Author(s):  
John Edward Ross Greenshields
Keyword(s):  
Germ Plasm ◽  
Female Parent ◽  
Early Embryo ◽  
Endosperm Nucleus ◽  
Interspecific Crosses ◽  
Primary Endosperm Nucleus ◽  
Embryo Abortion ◽  
Advanced Embryo ◽  
Essentially Normal ◽  
The Cross

Twelve species of Melilotus were intercrossed and the embryology of the hybrids was studied. The species involved in this study are M. alba, M. officinalis, M. suaveolens, M. polonica, M. dentata, M. altissima, M. hirsutus, M. taurica, M. messanensis, M. italica, M. sulcat, and M. speciosa. Among partially compatible crosses, M. officinalis × M. alba produces the most advanced embryo. Growth of the embryo proceeds normally until about eight days, and more slowly thereafter until the 12th or 13th day, when growth is completely inhibited and the embryo aborts. The reciprocal M. alba × M. officinalis embryo does not grow as large or differentiate as much before aborting by the 11th day. Other crosses, including M. officinalis × M. suaveolens and M. alba × M. messanensis form a normal proembryo that grows slowly to about the sixth day. The proembryo then loses polarity, organ development becomes abnormal, and the ovule aborts about the 12th day. Aborted embryos are also produced in the cross, M. alba × M. dentata. Reciprocal crosses of M. suaveolens and M. altissima and M. altissima × M. polonica produce essentially normal embryos up to eight days. These crosses may be sources of economically important germ plasm. Crosses of M. altissima × M. alba and M. italica × M. altissima exhibit early embryo abortion. The suspensor becomes necrotic in four or five days and the proembryo floats into the ovule cavity, which contains abundant noncellular endosperm. In the cross M. officinalis × M. altissima, neither the zygote nor the primary endosperm nucleus divides. When M. altissima is used as the female parent, the zygote does not divide but the endosperm proliferates. In the cross, M. italica × M. officinalis, neither the zygote nor the endosperm divides. Embryos of M. italica × M. sulcata grow for four or five days, but the primary endosperm nucleus does not divide. The hybrid seed of M. alba × M. suaveolens weighs less than seed of either parent. Although developing ovules are smaller than those of M. suaveolens × M. alba, the embryo of the former is much larger and more differentiated, and endosperm is more abundant. This relationship between these two compatible species is of particular theoretical interest. Although many of the crosses do not mature viable seed, some embryos develop normally to a point where they would be worthy subjects for culture on nutrient agar.

scholarly journals A MUTANT AFFECTING MEIOSIS IN NEUROSPORA

Genetics ◽  
1975 ◽  
Vol 80 (1) ◽  
pp. 125-133
Author(s):  
David A Smith
Keyword(s):  
Linkage Group ◽  
Meiotic Division ◽  
Group Iv ◽  
Black Pigment ◽  
Crossing Over ◽  
Wild Type ◽  
Linkage Groups ◽  
Recessive Mutant ◽  
Ascospore Production

ABSTRACT Many mutants affecting meiosis increase the occurrence of aneuploid meiotic products. In Neurospora, mutants of this type cause ascospore abortion which is reflected by an increase in the proportion of ascospores failing to develop black pigment. The usefulness of the criterion white-ascospore-production as a signal for the presence of a mutant affecting meiosis is demonstrated by the recovery of several such mutants. One of these is mei-1 (meiotic-1), a recessive mutant on linkage group IV. Crosses homozygous for mei-1 produce 90% white ascospores (vs. 5% in wild-type crosses). Viable ascospores, invariably black, are always disomic for one or more linkage groups; the chromatids assorted into viable ascospores do not engage in crossing over in meiosis. The distribution of viable ascospores in individual asci suggests that all meioses are defective in the first meiotic division, and that most meioses are defective in both divisions.

Fertilisation of polar nuclei and formation of early endosperms in Dendrobium catenatum: evidence for the second fertilisation in Orchidaceae

2018 ◽  
Vol 66 (4) ◽  
pp. 354 ◽  
Author(s):  
Yong Chen ◽  
Chu Zhang ◽  
Xiao-feng Wang ◽  
Cheng-qi Ao
Keyword(s):  
Embryo Development ◽  
Endosperm Development ◽  
Endosperm Nucleus ◽  
Primary Endosperm Nucleus ◽  
Section Technique ◽  
Embryo Stage ◽  
New Evidence

Whether the second fertilisation, i.e. fertilisation of polar nuclei, or fusion of the second sperm with polar nuclei occurs in Orchidaceae has long been controversial because of lack of evidence. In the present study, we observed fusion and fertilisation of polar nuclei and formation of early endosperms in the orchid Dendrobium catenatum Lindl., by using a resin-embedded section technique. As the product of the second fertilisation, the primary endosperm nucleus (fertilised polar nuclei) can last until the global embryo stage, indicating that initiation of endosperm development and that of embryo development were fully asynchronous. The present study demonstrated the occurrence of the second fertilisation in D. catenatum by providing lines of new evidence.

Mating Within the Meiotic Tetrad and the Maintenance of Genomic Heterozygosity

Genetics ◽  
2004 ◽  
Vol 166 (4) ◽  
pp. 1751-1759 ◽  
Author(s):  
Michael E Hood ◽  
Janis Antonovics
Keyword(s):  
North America ◽  
Meiotic Division ◽  
Genetic Load ◽  
Size Variation ◽  
Linkage Groups ◽  
Tetrad Analysis ◽  
Linear Tetrad ◽  
Pcr Products ◽  
Dynamic Genome ◽  
Diverse Groups

Abstract Mating among the products of a single meiosis (automixis or meiotic parthenogenesis) is found in diverse groups of plant, animal, and fungal taxa. Restoration of the diploid stage is often strictly controlled and brings together products separated at the first meiotic division. Despite apparent similarities to diploid selfing, the theoretical prediction is that heterozygosity should be maintained on all chromosomes when it is linked to the centromeres and thus also segregates at the first meiotic division. Using the fungus Microbotryum, we directly test this prediction by linear tetrad analysis. The patterns of meiotic segregation for chromosome size variation (electrophoretic karyotypes) and PCR products (AFLP procedures) were determined for Microbotryum lineages native to North America and Europe. Our data reveal a surprisingly dynamic genome that is rich in heterozygosity and where size-dimorphic autosomes are common. The genetic variation agrees with the prediction of centromere-linked heterozygosity. This was observed to the greatest extent in the lineage of Microbotryum native to North America where there was consistent first-division segregation and independent assortment of multiple linkage groups. The data also show properties that distinguish the fungal sex chromosomes from the autosomes in both lineages of Microbotryum. We describe a scenario where the mating system of automixis with first-division restitution is the result of feedback mechanisms to control exposure of genetic load.

Reproductive success, spontaneous embryo abortion, and genetic load in flowering plants

Oecologia ◽  
1987 ◽  
Vol 71 (4) ◽  
pp. 501-509 ◽  
Author(s):  
D. Wiens ◽  
C. L. Calvin ◽  
C. A. Wilson ◽  
C. I. Davern ◽  
D. Frank ◽  
...  
Keyword(s):  
Reproductive Success ◽  
Genetic Load ◽  
Flowering Plants ◽  
Embryo Abortion

Capsella Embryogenesis: The Central Cell

1973 ◽  
Vol 12 (3) ◽  
pp. 741-763
Author(s):  
PATRICIA SCHULZ ◽  
W. A. JENSEN
Keyword(s):  
Central Cell ◽  
Endosperm Nucleus ◽  
Binucleate Cell ◽  
Cell Cytoplasm ◽  
Primary Endosperm Nucleus ◽  
Structural Reorganization ◽  
Nucleolar Material ◽  
And Function ◽  
Relationship Of ◽  
The Relationship

The central cell is the binucleate cell of the angiosperm megagametophyte which contains the polar nuclei and participates in double fertilization. The structure of the mature central cell, the fusion of the polar nuclei and the primary endosperm nucleus were studied with the electron microscope. The central cell cytoplasm appears very active and has an extensive ER, many mitochondria, dictyosomes, microbodies, polysomes, chloroplasts with well developed grana and starch and lipid reserves. A single, giant mitochondrion appears in the cytoplasm near the polar nuclei at the time of fertilization, but its origin, fate and function are not known. Cytoplasmic aggregates of dense, granular material are associated with the primary endosperm nucleus and structurally resemble the nucleolus and similar aggregates in the nucleoplasm. It is suggested that these cytoplasmic perinuclear bodies may represent extruded nucleolar material. The central cell cytoplasm does not undergo any notable structural reorganization as a result of fertilization. The relationship of the central cell to the other cells of the mature megagametophyte and its possible role in embryogenesis is discussed.

Anatomy of Flowering Plants

2020 ◽  
Author(s):  
Paula J. Rudall
Keyword(s):  
Flowering Plants
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